1. Purpose of the Invention
This invention relates in general to certain new and useful improvements in a power control for hot gas engines, and, more particularly, to differential-type mechanism power controls for hot gas engines which adjust the phase angle between a displacer section and the expander section of the engine.
2. Brief Description of the Prior Art
Hot gas engines, often referred to as "Stirling" engines, have been known for a long period of time. Generally, the Stirling engine comprises a pair of pistons, including an expander piston and a displacer piston, both of which are connected to a single crankshaft. A heat exchanger is connected between the expander portion of the engine and the displacer portion of the engine. In the expander portion of the engine, hot gas is expanded and converts heat energy into power, so that the overall engine produces a useful power output. The displacer portion of the engine utilizes some of the power from the crankshaft to compress a cool, working gas, thereby generating a net power output from the engine.
The typical Stirling engine is constructed so that a fixed and predetermined phase angle exists between the expander power piston and the displacer piston in the engine. When the phase angle between the displacer piston and the expander power piston is 0.degree., there is no power output from the engine. Increases in a positive direction of the phase angle between the displacer piston and the expander piston results in a net forward power output from the engine. Correspondingly, a phase angle change in the opposite direction results in a net reverse power output. Thus, at a full 90.degree. phase angle difference between the expander piston and the displacer piston, full forward power is obtained, and with a -90.degree. phase angle between the expander piston and the displacer piston, full reverse power is obtained from the engine. In this way, it is possible to control the engine's power output and also to change the output to a forward or reverse direction.
There have been many proposed devices to change the phase relationship between the expander portion and the displacer portion of the Stirling engine. In general, a relatively large amount of power is required to overcome the reaction forces acting between the displacer portion and the expander portion of the Stirling engine. The power requirements of any mechanism to change the power rating of the engine affects the normal power transmitting ability. Thus, any mechanism to change the phase between the expander portion and the displacer portion must meet various power requirements with minimum torque and speed levels. In addition, the size, weight and cost of the mechanism to change the phase between the expander portion and the displacer portion must be kept at a minimum. It has been well recognized that an efficient and simple mechanism for changing the phase between the expander portion and the displacer portion of the Stirling engine in order to vary engine power output and drive direction will significantly increase the efficiency of the engine and lend to added commercial application thereof.
There have been several proposed phase changing devices in the prior art, as for example, that illustrated in U.S. Pat. No. 3,315,465 to Wallis in which a variable ratio transmission is connected in a single in-line crankshaft constituting a part of the power train of the engine. The expander piston of the engine operates on the crankshaft and the displace piston is operable thereby. Another form of control device for use with a hot gas engine is disclosed in U.S. Pat. No. 3,416,308 to Livezey which employs a complex planetary gear arrangement, including concentric drive shafts and a servo motor required to enforce the changed phase relationship. A further form of phase change control device for use with a hot gas engine is disclosed in U.S. Pat. No. 2,508,315 to Van Weenen et al. In this case, the crank shaft operates in a vertical plane, and the change in phase relationship is accomplished by a lever and wormgear type arrangement. U.S. Pat. No. 2,465,139 to Van Weenen et al also discloses a phase change device for use with a hot gas engine in which the phase changer comprises an eccentric located on a rod arranged inside of a hollow crank shaft. In addition, U.S. Pat. No. 3,192,789 to savage discloses a bevel gear arrangement for transmission of power between shaft portions which are parallel but not coupled in the same plane.
Each of these aforementioned phase changing devices which are used with hot gas engines are relatively complex in their construction, thereby increasing the cost of manufacture and also with a resultant decrease in efficiency of operation. Moreover, each of these devices are large in size and impose considerable weight. Furthermore, and more importantly, a large amount of power is required to operate each one of the aforementioned phase changing devices.